I doubt he will choose a liberal. But maybe he will choose a person who may vote either way.
Personally I'd be happier to see a scientist rather than a Judge on the court. Judges seem able to interpret the law any way they like. So why not employ someone who isn't just an intepreter but who bases their decisions on actual facts.
So a scientist will, for instance, be sure to prefer evolutionary science over religious origin stories, or to support climate science over energy companies.
A scientist might also be interested in economics, and they might concern themselves with what works rather than theories which don't.
Let them perhaps be agnostic, so they aren't swayed by random religious arguments.
Also, maybe they might know some history, so they have some knowledge to which to refer.
Is Neil de Grasse Tyson available?